Good use? It's the one reason I keep my Xbox plugged in, I'd have gotten tired of Forza long ago otherwise.
For the people wanting to remove wings, check
this topic. I never did get around to listing the manufacturer logos however.
Also, would there be any interest in a compilation of tweaks made with this tool? I spent some time rebalancing the supercars, adding omitted modifications, fixing inaccuracies etc.
One example modification is the Saleen S7. I lowered the seemingly excessive downforce, rewrote the engine config as the torque curve was completely incorrect, then added the factory twin-turbo upgrade that makes 750hp @ 6psi, and a transmission upgrade with the S7TT's ratios. Unfortunately, the torque with the TT upgrade is slightly more than the real car makes, but otherwise it should be accurate.
Another example is the Merc-McLaren SLR. It now features the Brabus exhaust upgrade for 660hp, to which you can add parts to reach Renntech's two kits of 722hp and 740hp. The upgraded wheels are now 20", with width and tyre profile based on Renntech's standard SLR upgrade. It's also possible to cut more weight than before from the car, down to the 1350kg of the SLR 722 GT. Put together, these let the SLR keep up with the newly twin-turbocharged 612 Scaglietti (the kit based on Koenig's 550 Maranello system, making ~840hp) and the CL65 (which can be upgraded to Carlsson, Brabus or Renntech specification, or a 900hp combination of the three).
An example of the expanded engine swaps is the 2005 Mustang GT, which will now take all of the various Ford Modular blocks in Forza, from the 385hp naturally aspirated 5.4 to Koenigsegg's 655hp twin-supercharged 4.7. Also, all of the Mazda rotaries will fit in place of any other rotary, for example a Renesis-powered FC RX7 or an RX8 with a 13B-REW.
There are also tons of minor tweaks, such as making the Infiniti G35 and Nissan Skyline 350GT more identical (as they are the same car) and making the pre-02 and post-02 MR2 more different (as the later car has a six-speed, but both cars can have one fitted along with a 2ZZ motor from the Celica).
Enough of the wall of text, I need to write a concise changelog some time. The only problem I have is that the current ModCars.ca2 dates back to the first release of this tool, and for some reason has randomly swollen to 8mb (with the occasional 4mb version), gives a message of 'Decompression Error: Output Buffer Too Small' before each (successful) opening, and has decided to blank all files relating to the WRX STi Spec-C. Fortunately, I don't drive it, but if someone else wants the edits, I'll see if adding my modified XMLs to a fresh Cars.ca2 with 1.2 works.